tracking – Adjust tracking of strings

Au­to­mat­i­cally ad­just spaces be­tween sym­bols in words or
phrases to fit them into a spec­i­fied length. Any chain of
sym­bols (in­clud­ing spaces) in the cur­rent font may be treated.

Com­mands \track{<length>}{<string>}
(add space <length>, which may be <0, af­ter
each sym­bol of <string>),
\fit­track{<length>}{<string>} (make
<string> fit into width <length>,
which may be smaller than the orig­i­nal width) and
\ra­tio­track{<ra­tio>}{<string>} (as
\fit­track, with <length> re­placed by
<ra­tio> of the nat­u­ral length of
<string>).